Bell 412 start and performance questions

[windmill brake state]

For the 412 drivers out there; a couple of questions please.

Why is it on the start procedure, at 12% N1 the throttle is opened past the idle detent all the way open then back to the idle detent, the idle solenoid activated then the throttle is set just below idle? Why not just go to idle, activate the idle detent then set just below idle? Does it have anything to do with the inner workings of the fuel control unit?

My second question is what is the best angle climb speed and where is it written? I have been quoted 45kts however no reference. This speed seemed a little slow to me, given best rate of climb is 70kts.

Thanks very much for your help.

Cheers,

WBS,

[Matthew Parsons]

I believe the throttle use on start is to first ensure you're at the idle stop. Once there you don't want to be stuck there if you lose electrical power, so you roll the throttle back to just behind the stop and you can shut down even with a dead battery.

Best angle of climb is not well defined for a helicopter. For a fixed wing, it considers the vertical component of your thrust vector. A helicopter can climb at 0 airspeed, making an angle of climb of 90 degrees. For the Bell 412, if you're on instruments, keep the speed at 60KIAS or higher (its a limitation) and that will be pretty close to your best angle of climb.

Matthew.

[gulliBell]

Q. "Why is it on the start procedure, at 12% N1 the throttle is opened past the idle detent all the way open then back to the idle detent,..."

A. Don't know, never heard of that procedure, never seen it done like that before...all the way open??? why????

I've (inadvertently) had the throttle ever so fractionally slightly past the idle position before when it's lit off and it went very hot very quickly...reckon if I'd followed the procedure suggested here (throttle opened all the way then back to idle detent) then my tail boom would probably have been a molten mass of metal pooled on the ground. Now I start it with the throttle slowly being opened at 12% and it lights off nicely before you even get to the idle stop position. Then steadily wind it on a bit more as you go past the 2nd ITT peak. No need to back off the throttle at all.

[Turkeyslapper]

Yep...we advance the throttle open then back to the idle detent...there was a reason but bugger me if I can remember it... Never had a start even looking like being hot and I have seen guys in classics EPs etc use the same technique. Someone must know something!

Turkey

[Kerry Sceneburner]

yep, 12% then full open and then back to just behind the detent. Bell412 classic

[Aser]

gulliBell:
I've (inadvertently) had the throttle ever so fractionally slightly past the idle position before when it's lit off and it went very hot very quickly...reckon if I'd followed the procedure suggested here (throttle opened all the way then back to idle detent) then my tail boom would probably have been a molten mass of metal pooled on the ground.

You missed the throttle check before start-up then(also all the way to full-then all the way to close), not a problem with the start procedure sugested here.

Another version I've seen called "canadian start" :E is when you are low on battery, just doing the full open-close to idle and set just below idle BEFORE engaging the START switch, works fine.

[rcapiloto]

Aser,

what you call the "canadian start" is actually standard starting procedure on the Sikorsky S-58T, which uses the same turbine as 412's. If it works fine in one machine, why shouldn't it work fine on the other?

Regards

[Gomer Pylot]

The best angle airspeed is zero, or the windspeed, whichever results in a 90 degree climb, straight up. That's the best angle you can get, unless you consider a backward climb better. :8 This of course assumes enough available power for an OGE climb.

The only reason I know of for taking the throttle to full open is to insure that you know where the throttle is being set, and that there is no binding throughout the range. You want it under the idle stop before engaging the starter so you can take it to full off in the event of an electrical failure. If the battery gets too low during the start, and the temp starts going too high, you risk not having enough battery voltage to engage the idle stop solenoid, thus not being able to stop the fuel, resulting in a hot start. Below the stop, you can take the throttle to full off with no electrical power. But I've never heard of going to full throttle at 12% N1. You do that before initiating the start.

[Big Guy]

In the flight manual under the starting procedure is is Engine 1 Throttle --open to idle at 12% GAS PROD RPM (N1) minimum.

Engine 1 ITT --Monitor to avoid a hot start. ITT limits for different models not to exceed ITT limits If ITT continues to rise, abort start by activating idle stop release and rolling throttle fully closed. Starter should remain engaged until ITT decreases.

[soggyboxers]

rcapiloto,

Then you well know that on the S58T there is a mechanical stop, ground idle before you advance it through the mechanical detent when it becomes the flight idle stop. The Bell 412 EP doesn't have the same engines (though the 412 does) and all the 412s as with the 212 have an electrically activated idle stop release, so the systems are not quite the same. It's a shame Bell never adopted the Sikorsky system.

WBS,

As has been mentioned, the best angle of climb speed for any helicopter is 0 knots groundspeed, i.e., a vertical climb. However, in most cases this is not practicable as much of the time you will not have the power reserve to achieve it. In most twin engine helicopters, when they are being operated to performance class one limitations, the 2 speeds which are relevant are the best rate of climb speed which, as you say, is 70 knots for the Bell 412 and the take off safety speed, which for the Bell 412 is 45 knots. This is only relevant during the initial phase of the take off and is basically the speed at which the aircraft will maintain a rate of climb of 100 feet per minute and remain clear of obstructions by the prescribed amount in the event of a single engine failure after TDP up to 200 feet. At this point, the aircraft is accelerated to Vy for the remainder of the climb. Depending on which RFM you're using (FAA/JAA/UK) it's in the Category A or Class 1 supplement.

[idle stop]

Big Guy has it, as per the RFM.
It's a good idea (indeed, see RFM para 2-5) to check the throttle for full and free BEFORE the start, to note the 'engine' legend position of the throttle at the idle stop and then to open it to just below the idle stop at 12% or above, and with indications of engine oil pressure. (212 is the same, but rotors will also normally start to move before the throttle.) That way if you do get a voltage drop or have to close the throttle in a hurry, it's easy. Remember too, that on both the 212 and 412, if you are holding the throttle back against the idle stop, friction may result in the plunger not retracting when you operate the idle stop (solenoid) release. (As Note in RFM.)
Incidentally, I would advocate the same procedure for the AS350 with collective throttle and for the EC120.
As for 412 angle of climb, see the Class 1/Perf A segment at 45 KIAS, as someone else has pointed out.
Now I'm exhausted....all this 'idle stop' chat. (And no, the soubriquet has nothing to do with 212/412!)
Idle Stop.

[windmill brake state]

Thanks for all your responses guys.

WBS

[zudhir]

Hi. I'm a recent 412 convert. Tend to draw parallels to my previous helo- the ALH (Dhruv). I have a few queries. Grateful if anyone could help.

1. The 412 EP RFM in the Cat A supplement gives a graph that gives "Target Torque" which, say at 30 deg Sea Level, gives a target torque at 2.5 min rating of 65%. However in the limitations section, the OEI torque limit is supposed to be 81%. So what torque would I need to pull? And what is Target Torque???

2. For various ratings, there would be ITT, N1 and Torque limits. I presume the limit you hit first would be the limiting factor for that rating. So, at sea level around 30 deg C what limit would i hit first? No performance graphs let me analyse this.

[Troglodita]

So at sea level around 30 deg C what limit would i hit first? No performance graphs let me analyse this.

ITT always (940 degrees C on later p/n guages 920 degrees on earlier)

[aquila105]

I am with Mattew on this one. The reason why it is recommended to open the throttle all the way is that it is the only way you can be absolutely positive that you are passed the detent. Many experienced 412 pilots just open the throttle a tad on the right side of the detent and wait for the lightoff to prevent for getting stuck on the wrong side of the detent at the wrong time.

Note: I personally don't wait for the proverbial 12% to introduce gas. I do it as soon as I see positive oil pressure on the gage. It will happen always above 12% and it is a more critical start-no start decision item.

[Gomer Pylot]

Putting the throttle just below idle detent is the way I was taught, and the way I've always done it. If the battery dies on you during the start, and you're above the idle detent, you'll melt the engine, because you can't close the throttle. I've always opened the throttle full open, back to idle, check where that is, close the throttle, and then initiate the start, and at 12% open it to just below where you saw it at idle. With experience, you can open the throttle there without even looking, doing it by feel. PT6s start very benignly, and the exact location of the throttle isn't critical, unless the battery dies. And 412 batteries have been known to die during start.

[zudhir]

WBS,
Regarding climb angle speed, you remember the basic power curve? The tangent to the power required curve from the origin of the power available line gives the best climb angle speed. What this means is that:
1. The best climb angle is irrelevent when power available is more than power required. i.e. the best speed will be zero.
2. When power available is lesser, then the best speed will actually depend upon how much lower the power available is- lower the power avbl, higher the best climb angle speed

[helibuoy73]

Hi! Picking up an old thread.
At Sealevel 30degC, I thought the chances would be brighter for a drop in Nr as a result of N1 topping before anything else. Otherwise Tgt Tq of 67 or 73% wouldn't make sense?

One year back, the tgt tq graph was revised shifting the entire thing right. The tgt tq for say Sea level 30deg now has become about 73%.

I have a couple of queries based on this revision:

1. Now with the increased target torque available, shouldn't the chart giving the max permitted wt to hover with Single Engine also change / increase?

2. Consequently, should'nt the WAT graphs for Cat A operations also change and permit an increase in allowable AUW?

[IntheTin]

During my initial SIM training, I was taught the start procedure of full open at 12% then back all the way to just inside the idle stop.
Being new I asked the instructor why and he said it was purely a Bell directive. Didn't go into details though and I didn't think to ask! :ok:

[JHR]

During the mid 90's I flew with a Bell flight instructor in a BH212. His technique was to set the throttle just below the idle detent prior to engaging the starter. His explanation was it takes at least 12% N1 speed for the engine driven fuel pump to develope the required pressure to activate the fuel flow divider and primary start fuel nozzels. The company I work for has been using this start technique without a problem on both 212's and 412's for the last 17 years. I have witnesed another operator have a engine hot start using the Bell flight manual technique. After engaging the starter the throttle was rolled open above the idle stop, the battery voltage was to low to complete the start and to low to open the idle stop and abort the start.
Ouch!!

JHR

[spinwing]

Mmmm ...

212s & 412s(with -3B engines) and 412 EPs (with -3D?) engines certainly do start differently.

In the early days the so called 'Okanaghan' start was used because of the problem with the idle stop solenoid activation.

I understood that Bell in their wisdom modified the solenoid so it would operate reliably at a lower voltage but could be jammed by friction of the mechanism if an inexperienced pilot has an issue with the start routine.

After so many years and thousands of hours in the beasties ... (particularly with the 412EP) I now just do a check prior to start to ensure that the throttle IS in Idle Cut Off then hit the starter .... at >12% N1 gently roll the throttle to modulate the start ... the lightoff is gentle very much like with the -3B and under normal conditions acceleration good .... (if the battery or starter dies ... then there is no panic I just roll off back to ICO and all is well) as the monster goes through about 35-40% with a reasonable rate of acceleration I roll thru the stop to the idle position and at >55% disengage the starter .... simple ...


212 Vy was 54 Kts and the 412 around 70 Kts depending on Gross weight etc.


;)

[NewST]

I keep hearing all of the stories about how another operator had a problem with the batteries resulting in a hot start. Would really like to see an incident report that actually says that...

If you do not go above the idle stop and then release the stop and resest the throttle just below the idle stop, then you do NOT KNOW where the throttle is set. You are just guessing....

[212man]

Unless you have the delicay of a gorilla, the throttle cam pushing the idle stop is easy enought to feel and there should be no need to go past it.

Spinwing - the 212s I flew had a Vy of 56 kts :ok:

[lamanated]

see these?
Quiz Cards (http://www.freezingblue.com/iphone/flashcards/quiz.php?fileid=9320)

[Troglodita]

Engine starts


Bell Helicopters Textron has devised an alternate Engine Starting technique which has been adopted on all ******* operations. During the start procedure at 12%N1 with Engine Oil Pressure indicating, roll the throttle to slightly below the Flight Idle position (approx. 20 degrees - NG of ENGINE uppermost). If the ITT should rise rapidly during the start, control or "modulate" the temperature with the throttle. At approximately 45% N1, the throttle will need to be advanced slightly to increase the N1 to 61%.
This technique allows a pilot to abort a start at anytime with a simple "off" movement of the throttle to the cut-off position, even if electrical power fails.
Pilots must ensure correct internal battery or external power limitations prior to start.

Trog.

P.S Helibuoy - why would you worry about the WAT graphs for the FM Category A Runway (Part C) profile? you wouldn't ever consider using those - would you?

:8

[Shawn Coyle]

The only 'incident' I've ever heard of for the 'Throttle pre-positioned to just below idle before hitting start switch' method was when a very new-to-turbine engines pilot was partway through the start and had a loud buzzing noise in his headset. He immediately shut off the start switch without shutting off the throttle.
My friend sitting in the copilot seat watched the TOT go through the roof, and later picked up bits of melted engine off the tarmac. Needless to say, pilot was not long with the company.

[helibuoy73]

No, not Part C. My concern is Part A (Elevated helipads) for offshore ops.

[TunaSandwich]

The only 'incident' I've ever heard of for the 'Throttle pre-positioned to just below idle before hitting start switch' method was when a very new-to-turbine engines pilot was partway through the start and had a loud buzzing noise in his headset. He immediately shut off the start switch without shutting off the throttle.
My friend sitting in the copilot seat watched the TOT go through the roof, and later picked up bits of melted engine off the tarmac. Needless to say, pilot was not long with the company


Shawn, would the outcome not have been the same using any of the aforementioned methods?.

I wish Bell would clarify this issue, it seems every company I work for has a different start method, and then every pilot has his/her preferred method. I think just to say "refer to the 212/412 RFM" is unhelpful as this does not tell you 100% which side of the idle stop you are at. Two major companies I've worked for use the full open then back to just below idle stop method and I never heard of any problems. But listening to the reasoning of the alternative methods then the argument seems valid. No wonder there are issues with Hot starts, it can be very confusing for newly rated pilots being shown three different methods.

Of the three methods discussed, the only one that really makes sense to me is the so called "Canadian start". Apart from Shawn's example, does anyone know of any reason that this could not be used as standard?

TS

[helibuoy73]

My understanding is that for say Sea Level, 30deg C, deck at or above 90 ft ht when tgt tq was 67%, max Restd AUW was (and is) 11000 lbs.

Now that the tgt tq has increased to 73%, shouldn't there be a corresponding inc in Restd AUW?

[Troglodita]

Helibuoy,

The WAT Graph is only relevant for the climb segment above 200 feet and should not affect your Deck Operating weight.

Compare the graphs for the 3D, 3DE & 3DF engines on the EP - the WAT figures vary but the 2 and a half minute OEI parameter is the same for all 3 variants and this is the parameter used for segments 1 and segment 2 of the profile. Segment 3 (200 feet to 1000 feet) relies on the Max Continuous OEI for the 3D and the 30 minute OEI for the 3DE & 3DF which is why the WAT graphs differ.

For Offshore Ops most Operators use Twin Engine Hover out of Ground Effect (HOGE) graphs to calculate Landing and take-off Mass although the profile flown is similar if not identical to Cat A Part A.

We comply with Performance Class 2 and this is perfectly acceptable to all the Major Oil Companies that I have come across.

2 Engine HOGE for Unrestricted Decks (fully compliant with CAP437/ICAO Annex 14) gives the following figures:

For a basic 412 or 412SP with C Box Torque indication only your MTOM at 30 Deg C is 11400lbs.

For the 412HP or 412EP with Mast Torque indication your MTOM is 11900 at 30 Deg C.

For restricted decks - i.e. not fully compliant due to a whole range of factors we use HOGE minus 500 lbs to give extra power in hand.

Hope this is of some use.

Trog

[helibuoy73]

Thanks a ton Trog,

The basic difference is that where I'm operating right now ie; India, the DGCA has mandated that all offshore ops have to be Performance Class I (in vogue for more than 4yrs now).

Therefore Cat A, Part A kicks in restricting your load to WAT for Cat A Part A, which works out to 11000lbs (SL, 30deg C) for the EP with DF engines.

I guess this should be directly linked to the tgt tq (the tq that each DF eng is guaranteed to deliver OEI)?

[Troglodita]

Helibuoy,

What a waste of a 412 EP.

I haven't been too concerned with the CAT A (Part A) mainly cos' we don't have to be but I still as you do suspect the graphs.

I'll dig a bit deeper in the meantime.

Are you still doing your medical every morning? - What a place!

:ugh::ugh::ugh:

take care

Trog

[helibuoy73]

Trog,

Yeah Medical every mng (at least on paper) ;)

I'm looking for other places, but not been able to get my foot in, so far!

helibuoy

[prehar]

From what I have gathered so far the whole exercise of Performance Class I of DGCA is to talk Cat A but call it another name....unlike what most Oil companies worldwide follow as 'exposure time' during take off from Rigs etc ...to be able to climb away following a OEI condition..and maybe a similar exposure time during landings Offshore.
True Cat A capability for various machines like S-76 , AW-139 involves a great deal of concept definations,performance issues, helicopter configuration ,training for both Pilots from both seats(to land or take off from Offshore rigs based on obstructions etc ) which probably the DGCA would not like to address or is incapable of analysing with its present members .., nor would the helicopter Operators...so using part of the supplement for Cat A of the Bell 412 ,some details are reduced to some numbers that work for all concerned. I guess a similar number works for the Dauphin N3 or other such machines that operate Offshore.
Serious Regulators would go the extra mile to fully investigate , understand and legislate Cat A issues coz they are liable to legal recourse in many countries not only by the aggreived parties concerned ,but by Insurance companies as well... if they are found wanting .

[helibuoy73]

Absolutely!
My question remains, if the tgt tq has been revised (upwards), shouldn't there be a corresponding revision in the permissible RTOW?

[prehar]

Can you explain target torque and its origin ?...as in the Bell-412 Flight Manual ..Supplement details etc .
One could take a relook and try to understand what you say or question... else just quote verbatim all you see / cut - paste the whole page to better understand what the Bell company allows you to do or wants you to limit yourself to ?? Any data outside of the Bell Manuals I hope you understand is not legal .. except those which are introduced by Operators or Regulators to make Operations safer ?

[Shawn Coyle]

Prehar:
I'm sure there's something you'd like to know, but I'm afraid I don't understand your question!

[prehar]

Shawn,
You are the right person to help on the issue of Bell 412 Offshore Operations !!
I tried picking up an earlier post here.. of 18 Jun where Zudhir and helibuoy were trying to understand what is a 'target torque' and related MTOW issues in the Cat A supplement of the Bell 412 ....I don't readily have one so I can't fully understand their apprehensions .
Thanks
Prehar

[helibuoy73]

Shawn & Prehar,

Well here goes:

I had raised a query with Bell in Feb2009 as follows:


The basic RFM for
Bell 412 EP lays
down the engine torque limit of 81% for 2.5' OEI
operation.



FMS 56.3 & 56.4 for
30' power setting for DF engines retains the same 81% engine torque limit for
2.5' OEI operation.




If you look at the
performance graphs for Target Torque in FMS 62.3 & 62.4 (Cat A operations
with D series engines), the maximum 2.5' engine torque is only 73% at -40
degrees at Sea level. At 20 degrees and 30 degrees we get the figures of 67.5%
and 65%. Since the graph talks of Power Available for 2.5' OEI operation, does
it mean that the power limits of 77% (30') and 81% (2.5') are just figures that
can not be achieved?



Based on this query, I believe, the Tgt Torque graph was revised last year in Jul2009, shifting the entire graph right and also increasing the max limit to 81%.

With the revised graph the tgt tq has increased (ex 30deg C SL the fig has inc from 67% earlier to 73% now) and so on.

My quest is, with this inc in tgt tq shouldn't there be a corresponding inc in the RTOW for Cat A ops?

Helibuoy

[Buitenzorg]

My quest is, with this inc in tgt tq shouldn't there be a corresponding inc in the RTOW for Cat A ops?
As Troglodita has already answered you:

No.

The target torque is Bell’s poor man’s equivalent to a FLI (first limit indicator). Dependant on ambient conditions the first OEI limit the engine is expected to reach, whether engine torque, ITT or N1, is “translated” into a calculated torque value, so in case of an engine failure the pilot has only one power instrument to monitor at what will be a pretty busy time.

This target torque value represents the first OEI 2½ minute limit to be reached.

As Troglodita pointed out, the climb segment between 200 and 1000 ft AGL is the limiting segment in determining Cat A/PC1 RTOW, and this is flown/certificated at OEI MCP (-3D engines) or OEI 30 min. limits (-3DE and -3DF engines). So the target torque value has nothing to do with the power settings during the “weight limiting” segment of the Cat A profile.

Hope this answers your question adequately.

[helibuoy73]

As Troglodita pointed out, the climb segment between 200 and 1000 ft AGL is the limiting segment in determining Cat A/PC1 RTOW, and this is flown/certificated at OEI MCP (-3D engines) or OEI 30 min. limits (-3DE and -3DF engines). So the target torque value has nothing to do with the power settings during the “weight limiting” segment of the Cat A profile.



Well, I would agree to this for Performance Class 2, not for performance Class 1.
For Perf Cl 1, the limiting factor should be segment 1 ie; pickup - hover - OGE - TDP (Rotation). Therefore the RTOW should be linked to hover capabilty (almost) with OEI, and this shlould be linked to the Target Torque?

[212man]

HB73,
the first segment is between achieving Vtoss and 200 ft, when OEI. It is certainly not the limiting segment for the 212. For the Clear area Cat A profile, the TDP is 56 kts at 35 ft and this is then the subsequent Vtoss in the event of an engine failure. The predicated rate of climb is 100 ft/min using 2.5 minute power. However, 56 kts is also Vy - the speed at which the second segment is climbed at. This segment requires a 50% increase in rate of climb but at a reduced power setting - MCP OEI. There is no drag reduction from raising undercarriage either, unlike wheeled types.

Obviously, then, the second segment is the limiting factor for Class 1 Performance (using the clear area procedure.)

[helibuoy73]

I'm afraid that's not correct for Bell412.
RFM states

Segment 1 is defined as profile from takeoff to VTOSS and positive rate of climb.

[Buitenzorg]

For Perf Cl 1, the limiting factor should be segment 1
Where does it say that?

[HU500D]

:mad: Fly the damm thing, it's just a helicopter.

[helibuoy73]

The RFM does not say that for Perf Class I, the limiting factor is Segment 1. I was just saying what it defines 'Segment 1' as.

Power / Torque required is max in Segment 1, that is why I think that should be the limiting factor for RTOW and not segment 2 (Perf Cl 1). And this in turn should be linked to the target torque!

[helibuoy73]

Fly the damn thing, it's just a helicopter

Wouldn't it be nice if you could carry an extra passenger or two (safely and legally complying with all local regulations)?

There is a good deal of difference between 11,000lbs and 11,900lbs.

[JimL]

I am astounded at the lack of knowledge being illustrated by some on this thread (and have stayed off for that reason); you might improve your understanding of offshore profiles by reading the following thread (it also explains why PC1 is not always possible offshore):

http://www.pprune.org/rotorheads/405677-performance-class-two-enhanced-offshore.html

It would appear that only Bell use the three segment classification, most other manufacturers define: the first segment (100ft/min climb at Vtoss up to 200ft); the acceleration segment (level acceleration from Vtoss to Vy); and second segment (150ft/min climb from 200ft to 1000ft at Vy) - all at the appropriate power settings.

For offshore operations the first segment (as used by other than Bell) is never limiting as the departure sector has to be free of obstacles (operations with exposure might not use the CAT A procedure). The second segment climb is a constant for all procedures (and for PC1 and PC2).

Apart from the second segment climb, the manufacturer may configure any of the other elements to suit the operator's constraints - that includes: the defined manoeuvre to TDP (which can be horizontal, vertical or oblique and can be operated with a target Tq, a delta Tq or a target ROC); the rejected take-off distance; the take-off distance; and the first segment climb (the Vtoss can be defined by the manufacturer). Any of the elements of the profile may be limiting as they have to be calculated with respect to the obstacle environment of the operating site (which has to be known/surveyed).

A CAT A procedure only becomes 'an operation in PC1' when the environmental aspects of the operating site have been taken into account and the mass calculated/adjusted. It is the Operational Rule that sets obstacle clearance criteria, the CAT A data is used only to satisfy those rules!

Jim

[helibuoy73]

Jim,

Thanks for the link pointer. A very enlightening thread indeed!

If you could just indulge me a little longer- Shouldn't an increase in Tgt Tq result in an increase in RTOW/RLW for PC1?

HB

[JimL]

If you are talking about an offshore procedure, target/delta Tq is associated with the deck-edge clearance (as discussed in the thread shown) - this target/deltaTq will provide the vertical acceleration (ROC) that results in the energy for the rotation/deck-edge clearance manoeuvre.

In the limited winds and high temperatures associated with India, deck-edge clearance is unlikely to be the limiting condition, it is more likely to be the drop-down (which is associated with single-engine power).

As the wind increases (for a given engine setting) drop down decreases until the limiting condition becomes the second segment climb. None of this is entirely predictable because the helicopter/engine combinations are configured to favour one or another of the power setting.

The engine manufacturer can also 'make available' an additional power mode - this has already been discussed on this thread because the PT6 can come with a 30 minute power setting (or it can be limited just to the max continuous). Not all manufacturers provide the '30 second'/'2 minute' power modes - staying instead with a single 2.5 minute power setting.

So, in answer to your question; not necessarily!

Jim

[helibuoy73]

Thanks Jim,

Your explanation confirms my understanding.
As I understand, PC1 offshore, with ltd winds and high temps, average drop down from low floaters to 90-100 ft, the RTOW/RLW limiting factor is likely to be single eng capability. Tgt Tq, again linked to single engine capability. So both are directly/indirectly linked.
The increased tgt tq with same AUW, if nothing else, provides us with additional safety (albeit carrying load less than max perhaps possible PC1)

HB

[JimL]

Not quite - the RTOM/RLM are part of performance planning and have to be in accordance with: the procedure; deck-edge clearance; drop-down; and climb performance. The mass calculation could be from one graph or several.

The AEO target/delta Tq is associated with the necessity to produce an ideal set of conditions in the vertical climb - i.e. to ensure deck-edge clearance from rotation.

If an engine fails at or after TDP, the good engine will accelerate to topping (or, if there is a FADEC, the single engine limit) regardless of the AEO Tq set (if the target Tq is high, there will be rotor droop - which will have to be controlled); from that point the drop-down, continued take-off and climb segments will be with one-engine-inoperative.

The setting of that engine will have to be in accordance with the defined limits. With a modern FADEC controlled engine and a failure at the worst time, the 30 second limit will (likely) take the aircraft to the beginning of the first climb segment (if drop-down has been scheduled - into the water if not); the first climb segment (200ft at 100ft/min) will use up the two minute limit; leaving the second climb segment to be flown at the next level of limits.

With powerful aircraft like the AW139 or the Bell 429 it is likely that they could (in a temperate climate) reach 1000ft before the 2 minute power setting is exhausted.

All of these descriptions are with the failure at the worst time (which is one second before TDP when the Pilot Intervention Time (PIT) is set to that interval). Descriptions are general; your aircraft/engine type specific profile and procedures may differ in some way.

To conclude I would emphasize once again that PC1 is not always possible offshore (because of environmental conditions) and should not be part of any regulatory regime.

Jim

[helibuoy73]

Jim,

I think there is a difference in the Tgt Tq that we're discussing.
The tgt tq I'm talking about is the OEI tgt tq. The tq that the healthy engine is guaranteed to provide, if the eng satisfies the Power assurance check.
It is the tq that the pilot is advised to set initially in case of an OEI.
It should therefore have nothing to do with the deck clearance or AEO ROC.
However, when the tgt tq availability graph was revised upward last year, I was expecting the RTOW also to increase correspondingly.

HB

[JimL]

helibuoy73,

I see I have been guilty of not reading the thread thoroughly. I missed Buitenzorg's comment that clarified exactly what you have just said:The target torque is Bell’s poor man’s equivalent to a FLI (first limit indicator). Dependant on ambient conditions the first OEI limit the engine is expected to reach, whether engine torque, ITT or N1, is “translated” into a calculated torque value, so in case of an engine failure the pilot has only one power instrument to monitor at what will be a pretty busy time.
If you are using a CAT A helideck procedure in offshore operations, the RTOM is probably derived from two parts; the WAT part which covers the take-off profile (deck-edge clearance) and includes the first and second segment climb performance (no need to correct for obstacle clearance as the take-off segment has to be clear of obstacles) and that part which deals with the drop-down. It is likely that the drop-down portion will include wind accountability (which might have a cut-off value to prevent you exceeding the mass for the second segment climb, by using wind accountability to raise the mass).

As was previously explained, the deck-edge clearance part of the profile depends almost entirely of the energy provided by the AEO acceleration (and the higher Nr used in the take-off profile). Because the AEO Tq will be higher than the permitted OEI Tq, any failure will cause the remaining engine to go to topping - resulting in a rotor droop. Containing (restoring) the Nr will keep the engine at topping until you have reached a safe flying condition (usually just before the bottom of the descent - sometimes called Vt or target speed) at which time the engine is set to a lower limit (if 30 second power has been available) and a climb at Vtoss achieved.

Apart from adjusting the power to remove any condition of exceedence (caused by the engine moving away from its correct topping setting), the first time you have to adjust the setting will be to move from 30 second to 2 minute power (or, if there is no 30 second setting, from 2.5 minute to the next setting).

However, this still does not answer your question and that is because I can see no relevance of a Tgt Tq (as described by Buitenzorg) to an offshore profile. Perhaps your best bet then is to approach your Bell rep (there will be one in India) and pose the question to him/her.

You give the impression (from your comments) that in spite of the fact that you claim to be operating to PC1, you are not adjusting the masses for drop-down. Is that a correct assumption?

Jim

[helibuoy73]

Jim,

Thanks for the detailed reply.

You give the impression (from your comments) that in spite of the fact that you claim to be operating to PC1, you are not adjusting the masses for drop-down. Is that a correct assumption?



We are adjusting RTOW/RLW for drop down ht, as advocated by the RFM CatA supplement.
Drop down ht 90Ft or more, std WAT graph for Cat A Part A (elevated helipads) applies :- which gives say 30degC, SL, Nil winds - RTOW 11,000lbs. (Increases with head wind component).
If drop down less than 90ft, the reduction in RTOW is calc from dedicated graph for different drop down hts (less than 90Ft) which results in a even lesser RTOW.


A second question (I have a faint idea about the ans but not sure if it is correct)
Why do we beep up the Nr to 103% before takeoff / landing in CatA profiles?
As I understand, we are on the wrong side of the L/D ratio, so inc in Nr actually increases the Drag (therefore torque / power reqmt) more than the Lift. So what is the benefit? Is it just more reserve of Nr in case of an OEI?

HB

[JimL]

Anyone else wish to join the party and answer this?

Jim

[Senior Pilot]

Why do we beep up the Nr to 103% before takeoff / landing in CatA profiles?
As I understand, we are on the wrong side of the L/D ratio, so inc in Nr actually increases the Drag (therefore torque / power reqmt) more than the Lift. So what is the benefit? Is it just more reserve of Nr in case of an OEI?

That's what I was taught: 103%Nr gives you a reserve to allow for droop when recognising and responding to an engine failure. Much the same as A109E/S with the 102%Nr selection, for the same reason.

[212man]

When you are TQ limited it also improves the TQ margin - for a given hover power the TQ will decrease as Nr rises. I'm not sure that the L/D ratio does rise - the induced drag will decrease with the reduced pitch setting.

[spinwing]

Mmmmmm ....

And with the 412EP the increased Nr also gives you more T/R authority ... as well as improving the rotor disc area ... the 412 with 'slow' (read old) governors will cause a fair bit of coning which in turn can cause all sorts of RPM and therefore Tq oscillations (which the yaw SAS then tries to cure) ... the result is usually an 'Over Torque' !!


:ugh:

[helibuoy73]

When you are TQ limited it also improves the TQ margin - for a given hover power the TQ will decrease as Nr rises. I'm not sure that the L/D ratio does rise - the induced drag will decrease with the reduced pitch setting.
L/D. Cruise at say 75% tq. Beep down Nr to say 97%, tq reduces, inc pitch to get same tq 75%. You now get a higher speed. This led me to the conclusion reduced Nr is good for the L/D. Conversely Inc Nr is detrimental for L/D. I also understand designers design the aerofoil in a manner that dec Nr improves L/D so that in case of a droop in Nr at hover, due to overload or whatever, the pilot still has a chance of a get away.

Secondly, with all these benefits of 103% Nr :- Reserve Nr for droop, inc disc surface, inc TR effectiveness; are there any drawbacks too? Otherwise why have this for Cat A only? This additional safety, why not have it for all operations?

HB

[Aser]

helibuoy73, related thread about your last question:
http://www.pprune.org/rotorheads/189116-low-rrpm-cruise.html

regards
Aser

[helibuoy73]

Aser,

Thanks. Very interesting.

HB

[TunaSandwich]

Does anyone know how much voltage is needed to activate the idle stop release?

Would it be possible to reach 12%N1 and there not be enough juice to activate the release?

Happy New Year

[Shawn Coyle]

Tunasandwich:
It has happened during start, and is the reason for the various start procedures.
You certainly wouldn't want to get caught with the throttle above the idle stop, at below self-sustaining speed, and no voltage.

[Droopy]

A certain West African location, 1986, 212....pilot does start checks which involve full and free on the twist grips, idle release back to shutoff etc. Except he forgot to do the idle release bit, operated the starter and cracked open the fuel from ground idle upwards. :eek:

I was on leave at the time but I was told it was quite spectacular :uhoh:

[212man]

I once had a total electrics failure after the second engine start - some kind of short circuit - and found myself unable to shutdown from the cockpit! After some shouting across the cockpit to the co-pilot, I got out and opened the idle stop solenoids manually, to close the throttles. It's a strange sensation when it happens.

[Torquelimited]

Basic common sense logic must prevail and simply one should always monitor VDC voltage when engaging the starter and if the value dips below 15VDC and does not immediately begin to recover then just do not induce fuel.

[before landing check list]

When I flew the UH1 we routinely set the throttle just below the idle stop, the 212 also.

[gittijan]

The real problem is with less than 14V the Battery relays open, and you now have no voltage at all. Same thing with APU only if it decides to quit delivering voltage and you do not have the Battery switches on.

[wazz'n'zoom]

The DHFS Griffins (Bell 412 EP) have adopted the new 'throttle closed start procedure' and so far in one month, no incidents of messed up starts. The 'ginger beers' have placed an orange mark on the throttle barrel that is just below(approx 5mils) the idle stop and once at 12% N1 the throttle is moved to that mark. This, for the students, is very akin to the AS 350 that they flew prior to this except that they used a white dot on the collective. It makes an impressive whoosh as the flame is lit and a at low light/night, a blue flame flicks out the exhaust.
However, the new Hyd and Electrics check doesn't exercise the hyd switchover valve correctly and the check of the DC emergency load switch is sporadically dumping U/VHF radio pre-sets.
Happy days.

[gowaz]

wazz and zoom; you in when its dark?

[ashfaq.ghori]

Hi,

I just want to know what is Target Torque; and how to apply in real world.

As per RFM 412
TARGET TORQUE: Available 2½ minute OEl torque of minimum specification engine, assured by satisfactory completion of power assurance check.

As per Charts at sea level 23 degree C target torque is 73% for PT6T-3D/DE/DF

Now just a case that during takeoff Mast Torque used is between 75-81 or ever more as Twin Engine Operation. To be most unlucky OEI occur, so other engine take over. So Eng Torque will be same as Mast Torque (say at that time mast torque is 80), So Eng Torque = 80.

Now Torque is past the 73% that mean Target Torque limit (OEI) are crossed.

In real world 412 will never come to hover with max allowed weight at 73%

So I think I am missing something. Pls correct and help me in building better understanding.

Regards
Ashfaq

[longtime lurker]

Target torque is the minimum power that should be available from an engine (at the 2.5 minute OEI rating) that has passed a power assurance check.

It is a factor of density altitude.

The relevance of it depends on how you are operating.

For example, if you are correctly loaded (and rigged) as per the Category A supplement the target torque should be sufficient to enable you to:

Land back on the take-off area if the engine fails before TDP
Continue the take-off if the engine fails after TDP
Land at the intended landing area if the engine fails after LDP
Fly away if the engine fails before LDP

(if flown in accordance with the relevant profiles).

Similarly, Class D external load operations make use of the target torque figure in establishing whether you can maintain an OEI hover.

[Shawn Coyle]

lurker:
To be perfectly correct, the target torque is a factor of pressure altitude and temperature - a 5,000' Density altitude can be 9,000 PA and -40C or about 2,000' PA and +40C. The Target Torque would be vastly different in those two conditions.

[longtime lurker]

You are quite correct, thank you for pointing that. My apologies to the initial poster for being lazy and therefore misleading/incorrect in my reply.

[helibuoy73]

Ashfaq,

Practical application of tgt torque IMHO. If you have an OEI at high torque settings, one of the first actions would be to lower collective to restore / maintain rpm.
Lower, but how much, to what setting?
Too less, rpm would drop. Too much, you are not making optimum use of the power available from the good engine.
Target torque gives you a good guideline of min torque to which you can safely lower collective (Min assured torque) and then maybe come up a little, N1, Rrpm and ITT permitting, if the engine is giving a better performance (than the minimum assured by passing the PA).

HB

[ashfaq.ghori]

Thanks longtime lurker, Shawn Coyle and helibuoy73....for correcting me as I was having impression that Target Torque is my ceiling(upper Limit) for the OEI 2.5 min rating.

Now my understanding is lower limit for 2.5 OEI has changed but max remain 81% . Anytime my torque is in

59 - 73% = 30 min OEI setting (taking 30 degree C at sea level)
73 - 81% = 2.5 min OEI

as against
59 - 77% = 30 min OEI
77 - 81% = 2,5 min OEI

Correct me if wrong.

Also
As per definition of Target Torque its ........
TARGET TORQUE: Available 2½ minute OEl torque of minimum specification engine, assured by satisfactory completion of power assurance check.

So what exactly is ...satisfactory completion of power assurance check
because some engine may have +ve, 0 or -ve value, so is their any range for pass and fail.

As per my case my result for P.A. give me +40 and +25 (+-5 up and down).

Regards
Ashfaq

[helibuoy73]

3odeg C, SL, assured max tq you can get from the eng - 73% Not 81%

The 30 min and 2.5 min are more like txn limits and not eng limits. The max tq eng is assured (guaranteed) to produce is tgt tq (SL 30deg C, 73% for DF eng).

[Matthew Parsons]

To be most unlucky OEI occur, so other engine take over. So Eng Torque will be same as Mast Torque (say at that time mast torque is 80), So Eng Torque = 80.

Keep in mind that mast torque is not the sum of engine torques. Engine torque includes losses due to driving tail rotor, electrical system, generators, etc. Mast torque is the torque actually applied through the mast.

The conversion factor between mast and engine torque is listed in the flight manual, but is slightly dependant on a number of factors.

[heole]

Lots of interesting arguments and Shawn is right as usual about the Pressure..
Why the `Target Torque``?
First, It is an Engine Torque value, not a mast torque value.
Second: During Category A manoeuvres, following engine failure, different limits can be reached: the OEI can be limited by the Torque, the ITT or the NG.
In order to decrease the pilot workload following the engine failure at the decision point, test pilots have elected to use a single parameter to target . (So, you can focus your attention on only one gage, instead of monitoring 3)
At the targeted value, the engine parameters will not exceed any of the OEI limits and performances will be met. This target torque is based on a minimum spec engine performance
Whenever possible, (Ie: at Vtoss), If there is still some power available, the pilot can adjust the critical parameter (Torque, ITT or Ng) to the 2 ½ OEI limit.

[threesix]

there is really no issue here if you want to fully open the throttle and then go idle then click the detent and put it just below idle. In fact, i l learned to appreciate the value especially if ive just made a shutdown of engines and my passengers decided to board again after around 3 to 5 minutes. I just do the procedure however i doubled the position of throttle from the idle detent so as not to have a high ITT. Never had a problem after so many thousand starts...:)

[Blackopsrider7]

Hi 412EP pilots and maintainers. A friend of mine was doing a run up on a 412 Griffon, and this is what was happening. One Power Section(PS) was at 71% N2, he went to roll up the other PS and the one at 71% dropped down to 61% essentially idle. He reversed the PS's and tried it in the reverse order, and the power section at 71% again dropped to 61%. PS are PT6T-3Ds. What is your take on this? Thanks.

[212bushman]

G'day Bor7,
we had something similar to what you have. On our 3D's, the start sequence kept us guessing for a while. Whilst bringing up #2 eng, (#1 up & running). #1 would drop back to idle. We checked rigging , did PA's etc. Nothing out of the ordinary. Then we swapped AFCU's. Problem swapped , hence culprit found. (I am not sure why your snag alternates as per which one you bring up to match the 1st one up though)?
Hope this helps,
212bm.

[Blackopsrider7]

Thank you BM. I will tell the guys, to start there!

[Blackopsrider7]

Hi folks, we are having an issue with a B412EP that has PT6T-3D power sections. We can't seem to get our accel checks times down enough. What we have done so far is switched out the TCU(-01), cleaned the P-3 filters. Checked for air leaks. Our accel times are running around 6 secs to low of 4.99 so needless to say for the altitude and temps, we are not meeting our times. we have maxed out our dome adjustments( 6 clicks on this one) and only get a difference of 0.5 sec. This is both power sections, we did a power assuarnce and our temps are good, ITT margin is good...running out of options save switching out AFCU or bleed valves. Question two is will a -01 TCU cause issues with running -2 governors? There is a bullentin out, but for some reason we got our twin pac shipped like this. Any takers/advice on this one? Feel free to PM me.Thanks.

[Miamijerry]

Slow accel times, change the ACFU's.

-1 and -2, part numbered N2 gov's and TCU's can NOT be intermixed.

[cbox chip]

Is that to say that -1 and -2 N2 governors cannot be intermixed either?

[Miamijerry]

-1 N2 governors and -1 TCU are a set

and

-2 N2 governors and -2 TCU are a set

Don't mix -1 and -2

[erang5]

Hi all,

My company operates Bell 412SP with a BLR strake kit on their tail as well as early model a/c which are basically 212 with 4 blade rigid rotor which are called by some IGW ( Increased Gross Weight)
The so called IGW a/c have better hover and takeoff perf. (the basic weight is the same as the SP a/c). some pilots estimate the differences being more than 5% Tq

Does anyone have any insights as to why that might be?

I am also looking for hover performance charts as opposed to the max weight for hover that is provided in the civilian flight manual, any idea where to get such charts?

Thank you
Eran

[cbox chip]

Well the 412 "classic" has a smaller fuel system than the SP (5 cells versus 8) so I suppose it might be a bit lighter but I really can't imagine how it would outperform the newer bird with strakes (but no fast fin?)

Does the straight 412 read mast torque or is it the same as a 212 where it takes the total of the two single engine torques read at the c/box?

I don't know how it is on 412's but on 212's the difference between a good set of M/R blades and a bad set can be quite noticeable.

What are the empty weights of these machines?

[erang5]

cbox,

Thanks for your reply

as far as i know the Tq measure system is identical to the latter classic 412. It is same as the engines (PT6-3B) and lifting system...

Since we have 2 a\c of each type and they act quite similar I don't suspect malfunction

GW is the same despite the empty wight differences

[Encyclo]

Just the facts :8

412 'classic' has five fuel cells, similar to the 212 and holds roughly 220 Gal.
412 SP/HP/EP has 10 cells, six in the floor, four in the back for about 330 Gal

The 412 'Classic' and 412SP use the torquemeters off the Cbox to read torque, eng1 + eng2= MGB Tq

The 412HP/EP use torquemeter for eng Tq but phase shift mast for mast Tq, so eng1 + eng2 is not necessary equal to mast Tq.

Typically, worn/eroded blades don't have a big effect on performance for the 412; what you see in the charts is what you get.

Back to my coffee :ok:

[cbox chip]

Interesting info there. So the 412 linefrom oldest to newest goes 412 classic, 412SP, 412HP then 412EP?

So many variants jeez there's only one 212 ( well I guess two if you consider the HP kit). What I meant about good and bad blades was more how well a particular set flew together not age or erosion damage.

[Encyclo]

Roger that Cbox,

I have heard of an operator swapping a set of 212 blades to compare; same day same helicopter and measured about 500 Lbs more capacity for the same torque.

Haven't heard of that with 412s :(

[Chickenpool]

Why before start engine,pilot must RPM INCR/DECR switch........DECR FOR 8 SECONDS?
and what is 8 second ?

Thank you for answer :)

[Ascend Charlie]

So that the N2 beep is fully down before you get to open the throttles fully. This can prevent an overspeed in some cases - it may have been accidentally beeped all the way up while the engines were off.

And 8 seconds is 2 seconds less than 10 seconds...

[Chickenpool]

thank you for answer:) and relax (++!)